Caps are used to seal containers for at least two reasons. First, for many applications it is desirable to keep unwanted materials or contaminants that are outside of the container from entering into the container, which thereby prevents the contents of the container from becoming contaminated. Second, it is important in some applications to prevent the contents of the container from escaping from the container, which thereby prevents contamination of the surrounding environment by the contents of the container.
Many container caps function as a plug or seal for the reasons discussed above. However, it is desirable in certain applications to allow various components to enter into the container, and conversely, to allow these same or other components to exit from the container. More specifically, a sealed container may develop a pressure imbalance with the surrounding environment, such as an underpressure or an overpressure condition within the container. Many caps are not vented and can not exhaust gases from or receive gases into the container to relieve the underpressure or overpressure condition in the container. This may create problems.
For example, an overpressured container with a ventless cap may burst. Thus, a ventless cap is not desirable for a gasoline tank, such as on a car, because the tank presents a safety hazard if it becomes pressurized and ruptures. On the other hand, a cap that vents continuously may allow an overabundance of volatile components to escape from the container into the surrounding environment. In this manner, either the valuable contents of the container are lost, or the surrounding environment is contaminated by the evaporating contents of the container. Thus, a continuously venting cap is not desirable for a gas tank, as the gas tends to evaporate and harm the surrounding atmosphere.
Thus, in some applications it is preferred to have a cap that vents only when necessary, and is sealed at other times. However, these caps tend to have other problems that prevent or discourage their use in some applications, such as on a gas tank, as mentioned above. For example, these types of caps are often constructed from more than one type of material or from materials that are not easily separated, adding complexity to the fabrication and manufacture of the caps. Additionally, the recycling process for such a cap tends to require extra steps to separate the different materials used to make the cap. These additional steps tend to make recycling the cap less attractive, due to the additional cost of material separation before recycling.
Thus, there is a need for a ventilating system composed of recyclable or readily separable components.